linux-kernel - Re: [PATCH v3 2/4] net: stmmac: dwmac-qcom-ethqos: Mask PHY mode if configured with rgmii-id

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Message-ID: <30450f09-83d4-4ff0-96b2-9f251f0c0896@kernel.org>
Date: Tue, 21 Jan 2025 13:47:55 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Yijie Yang <quic_yijiyang@...cinc.com>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Vinod Koul <vkoul@...nel.org>,
 Maxime Coquelin <mcoquelin.stm32@...il.com>,
 Alexandre Torgue <alexandre.torgue@...s.st.com>,
 Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konradybcio@...nel.org>,
 Richard Cochran <richardcochran@...il.com>
Cc: netdev@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
 linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 2/4] net: stmmac: dwmac-qcom-ethqos: Mask PHY mode if
 configured with rgmii-id

On 21/01/2025 08:54, Yijie Yang wrote:
> The Qualcomm board always chooses the MAC to provide the delay instead of
> the PHY, which is completely opposite to the suggestion of the Linux
> kernel.

How does the Linux kernel suggest it?

> The usage of phy-mode in legacy DTS was also incorrect. Change the
> phy_mode passed from the DTS to the driver from PHY_INTERFACE_MODE_RGMII_ID
> to PHY_INTERFACE_MODE_RGMII to ensure correct operation and adherence to
> the definition.
> To address the ABI compatibility issue between the kernel and DTS caused by
> this change, handle the compatible string 'qcom,qcs404-evb-4000' in the
> code, as it is the only legacy board that mistakenly uses the 'rgmii'
> phy-mode.
> 
> Signed-off-by: Yijie Yang <quic_yijiyang@...cinc.com>
> ---
>  .../net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c    | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c
> index 2a5b38723635b5ef9233ca4709e99dd5ddf06b77..e228a62723e221d58d8c4f104109e0dcf682d06d 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c
> @@ -401,14 +401,11 @@ static int ethqos_dll_configure(struct qcom_ethqos *ethqos)
>  static int ethqos_rgmii_macro_init(struct qcom_ethqos *ethqos)
>  {
>  	struct device *dev = &ethqos->pdev->dev;
> -	int phase_shift;
> +	int phase_shift = 0;
>  	int loopback;
>  
>  	/* Determine if the PHY adds a 2 ns TX delay or the MAC handles it */
> -	if (ethqos->phy_mode == PHY_INTERFACE_MODE_RGMII_ID ||
> -	    ethqos->phy_mode == PHY_INTERFACE_MODE_RGMII_TXID)
> -		phase_shift = 0;
> -	else
> +	if (ethqos->phy_mode == PHY_INTERFACE_MODE_RGMII_ID)
>  		phase_shift = RGMII_CONFIG2_TX_CLK_PHASE_SHIFT_EN;
>  
>  	/* Disable loopback mode */
> @@ -810,6 +807,17 @@ static int qcom_ethqos_probe(struct platform_device *pdev)
>  	ret = of_get_phy_mode(np, &ethqos->phy_mode);
>  	if (ret)
>  		return dev_err_probe(dev, ret, "Failed to get phy mode\n");
> +
> +	root = of_find_node_by_path("/");
> +	if (root && of_device_is_compatible(root, "qcom,qcs404-evb-4000"))

First, just check if machine is compatible, don't open code it.

Second, drivers should really, really not rely on the machine. I don't
think how this resolves ABI break for other users at all.

You need to check what the ABI is here and do not break it.

Best regards,
Krzysztof